[Numpy-discussion] Re: Bypassing a[2].item()?

Travis Oliphant oliphant at ee.byu.edu
Thu Apr 20 20:16:02 CDT 2006


Robert Kern wrote:

>Ryan Gutenkunst wrote:
>  
>
>>On Apr 20, 2006, at 5:18 PM, Robert Kern wrote:
>>
>>    
>>
>>>Ryan Gutenkunst wrote:
>>>      
>>>
>
>  
>
>>>>2) If not, is it possible to get a "pure" scalar directly from an array
>>>>in one function call?
>>>>        
>>>>
>>>float(x[0]) seems to be faster on my PowerBook.
>>>      
>>>
>>It's faster for me, too, but float(x[0]) is still much slower than using
>>Numeric where x[0] suffices. I guess I'll just have to warn my users
>>away from the new scipy until numpy 0.9.8 comes out and scalar math is
>>sped up.
>>    
>>
>
>For that matter, a plain "x[0]" seems to be about 3x faster with Numeric than numpy.
>
>  
>
We are already special-casing the integer select code but could 
special-case the getitem code so that if nd==1 a faster construction is 
used.  I think right now a 0-dim array is being created only to get 
destroyed later on return.   Please add a ticket as this extremely 
common operation should be made as fast as possible. 

This is a little tricky because array_big_item is called in a few places 
and is expected to return an array.  If it returns a scalar in those 
places segfaults can occur.  Either checks need to be made in each of 
those cases or the special-casing needs to be in array_big_item_nice.  
I'm not sure which I prefer....

-Travis







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